1. Field of the Invention
This invention relates generally to speed reduction systems and, more particularly, to compact speed reduction systems usable for driving the tuning indicator dial of a UHF tuner.
2. Description of the Prior Art
Modern UHF television tuners generally employ a continuously variable tuning mechanism driven by a multiple turn detented selector shaft. The selector shaft of modern UHF tuners is generally rotatable over a range of approximately 7 revolutions to cover the seventy UHF channels, each revolution of the selector shaft covering 10 of the 70 channels. One form of tuning indicator which is used with UHF tuners of this type is rotatable over only 1 revolution, thereby requiring a speed reduction mechanism between the selector shaft and the tuning indicator dial.
Several speed reduction mechanisms for driving an indicator dial are known. These mechanisms generally employ a plurality of gears to achieve the desired speed reduction. Although these mechanisms provide a way to realize the necessary speed reduction, gear mechanisms are generally expensive and difficult to fabricate, tend to be bulky, and the play normally occurring between the gears can result in an erroneous indication by the indicator dial. The bulk of gear mechanisms is particularly objectionable in compact portable television sets where space is at a premium, thereby making it difficult to fabricate a satisfactory dial drive mechanism.
Flexible spline speed reduction mechanisms provide a compact speed reduction mechanism that avoids the problems of most other drive systems. For this reason, they have been used as speed reduction mechanisms for fine tuning UHF television tuners. However, flexible spline speed reduction mechanisms tend to bind with reduction ratios of much less than approximately 20-to-1 (the ratio used in fine tuning systems) are employed, and have been considered unsuitable for dial drive mechanisms where a 7-to-1 ratio is required.